Thermosetting coating composition

ABSTRACT

Novel solvent-based thermosetting composition comprising (a) hydroxy functional epoxy ester resin of number average molecular weight (Mn) between about 1,000 and about 5,000, comprising the reaction product of diepoxide with dicarboxylic acid and acid component comprising hydroxy functional acid and optionally further comprising fatty acid; and (b) polyfunctional, hydroxy-reactive crosslinking agent, for example, aminoplast crosslinking agent or blocked polyisocyanate crosslinking agent comprising isocyanate groups blocked by reaction with an active hydrogen bearing blocking agent. Coating composition may be formulated as primer sprayable with conventional spraying equipment.

TECHNICAL FIELD

This invention relates to a novel, solvent-based, thermosetting epoxyester coating composition. It relates also to such coating compositionformulated, for example, as sprayable coating composition suitable foruse as an automotive vehicle primer to make coatings which are highlyresistant to corrosion, humidity and solvents.

BACKGROUND

Solvent-based coating compositions are known which can be applied to asubstrate, for example, by spraying, and then cured by baking the coatedsubstrate at an elevated temperature suitable to drive off the organicsolvent and to promote crosslinking reaction. The resulting thermosetcoating, if sufficiently humidity and solvent resistant, can provideaesthetic and functional advantages including corrosion protection forthe underlying substrate.

It is an object of the present invention to provide solvent-basedthermosetting coating compositions comprising hydroxy functional epoxyester resins which are crosslink able during cure, on the surface of asubstrate.

It is another object of the invention to provide a method of making acoating on a substrate, which coating provides advantageous physicalproperties including, for example, humidity and solvent resistance andcorrosion protection for the underlying substrate. Additional aspectsand advantages of the invention will be apparent from the followingdescription thereof.

DISCLOSURE OF THE INVENTION

According to the present invention, a novel organic solvent basedcoating composition, in addition to solvent and any pigments andadditives such as, for example, catalyst, flow control agents and thelike, comprises:

(A) crosslinkable hydroxy functional epoxy ester resin preferably havinga number average molecular weight (Mn) between about 1,000 and about5,000 and comprising the reaction product of diepoxide chain extendedwith dicarboxylic acid and either subsequently or simultaneously chainterminated with acid component comprising hydroxy functional acid; and

(B) polyfunctional, hydroxy-reactive crosslinking agent selectedpreferably from aminoplast crosslinking agent such as, for example,hexamethoxymethyl melamine, and blocked polyisocyanate crosslinkingagent including, but not limited to, blocked trifunctional isocyanuratering containing polyisocyanates and oligoester modified blockedisocyanates, or a compatible mixture of any of them.

Particularly preferred compositions of the invention are those adaptedto be applied by spraying onto a substrate. Such compositions areespecially useful as a primer coat on the bare, unpolished metal surfaceof an automotive vehicle body panel.

According to another aspect of the invention, a method of making acorrosion, solvent and humidity resistant coating on a substratecomprises applying to the substrate the solvent based thermosettingcoating composition of the invention and subsequently subjecting thecoating to an elevated temperature for a time period sufficient tosubstantially cure the coating layer. Typically, the novel coatingcompositions of the invention can be cured by heating to between about240° F. and about 400° F., for a time period sufficient to yield a curedcoating, for example for about 10 to about 60 minutes. According topreferred embodiments of the invention, the coating composition can besufficiently cured for good coating properties by heating to about 240°F. for about 20 minutes but, in addition, such preferred compositionwill tolerate curing at up to about 400° F. for as much as about 60minutes without substantial loss of such advantageous coatingproperties.

The coating compositions of the present invention provide cure-responseadvantages without sacrifice of advantageous physical properties in thecured coating. That is, when applied, for example, over a metallicsubstrate, such as when applied as an automotive vehicle primer coatover sheet steel, cured coatings according to the invention have beenfound to provide excellent adhesion to the substrate, excellent humidityresistance, and excellent corrosion resistance.

Other features and advantages of this invention will become moreapparent from the following, detailed description thereof including thepreferred embodiments and the best mode of carrying out this invention.

DETAILED DESCRIPTION OF THE INVENTION

The hydroxy functional epoxy ester resin employed in the composition ofthe present invention preferably has a number average molecular weight(Mn) of between about 1,000 and about 5,000. More preferably, especiallyfor use in sprayable coating compositions of higher solids content, theepoxy ester resin has a number average molecular weight (Mn) of betweenabout 1000 and about 3000. The hydroxy functional epoxy ester resin isformed by reacting diepoxide with dicarboxylic acid to yield a diepoxidefunctional chain-extension reaction product and either simultaneously orsubsequently reacting such diepoxide reaction product preferably inapproximately 1 to 1 equivalent ratio with acid component comprisingprimary hydroxy functional acid in chain terminating reaction.

Thermosetting compositions of the invention comprise such epoxy esterresin and polyfunctional hydroxy-reactive crosslinking agent selected,preferably, from aminoplast crosslinking agent, blocked polyisocyanatecrosslinking agent comprising at least two isocyanate groups blocked byreaction with an active hydrogen bearing blocking agent. Thepolyfunctional crosslinking agent is included in the composition in anamount sufficient to provide between about 0.5 and about 1.6 reactivegroups per hydroxy functionality of the epoxy ester resin.

Each of the above major components of the compositions as well asoptional components and other aspects of the invention are describedhereinafter in greater detail.

A. Epoxy Ester Resin

As described above, the hydroxy functional epoxy ester resin is formedby reacting diepoxide, which has been chain extended with dicarboxylicacid, with acid component comprising primary hydroxy functional acid inchain terminating reaction.

(i) Diepoxide Reactant

The diepoxide reactant suitable for preparing the hydroxy functionalepoxy ester resin can be any of numerous diepoxides including many whichare commercially available and which will be apparent to the skilled ofthe art in view of the present disclosure. While, ultimately, the choiceof diepoxide reactant for preparing the hydroxy functional epoxy esterresin will depend to an extent upon the particular application intendedfor the final coating composition, terminal diepoxides, that isdiepoxides bearing two terminal epoxide groups, are generally mostpreferred. These are generally more reactive and therefore requiremilder reaction conditions under which undesirable side reactions, forexample, epoxy-epoxy reactions and gelation, can be more easily avoided.

Preferably, the diepoxide has a number average molecular weight (Mn)between about 100 and about 1000, and more preferably between about 100and about 600.

Suitable diepoxide reactants include, for example, bisphenol-Aepichlorohydrin epoxy resins such as the Epon (trademark) series, ShellChemical Company, Houston, Tex., and the DER (trademark) series, DowChemical Company, Midland, Mich. These dilglycidyl ether bisphenol-Aresins and higher molecular weight analogs thereof, are preferred inview of their low cost and commercial availability.

Also suitable are cycloaliphatic diepoxy resins such as, for example,the Eponex (trademark) series, Shell Chemical Company, Houston, Tex.;hydantoin epoxy resins such as, for example, Resin XB2793 (trademark),Ciba-Geigy Corporation, Ardsley, N.Y.; and any of a wide variety ofacyclic or cyclic aliphatic diepoxides such as, for example,1,4-butanediol diglycidyl ether and 4-vinylcyclohexene dioxide and thelike. Other suitable diepoxides, are commercially available or arereadily prepared by those skilled in the art and will be apparent to theskilled of the art in view of the present disclosure. Also, it will beunderstood from the foregoing that any mixture of compatible diepoxidesmay be used.

In addition to the diepoxide, a portion of the epoxy functionality canbe provided by any compatible monoepoxy compound or polyepoxy compoundor mixture of such compounds. Suitable polyepoxides include, forexample, those of molecular weight about 200 to about 800. Thepolyepoxide can be any of the well known types such as polyglycidylethers of polyphenols. These can be produced by etherification ofpolyphenol with epihalohydrin in the presence of alkali. It will berecognized by the skilled of the art in view of the present disclosure,that in some instances, particularly where a coating composition of highsolids content is less important, it may be desirable to incorporatepolyepoxide of higher molecular weight. Preferably, any such polyepoxidecontains free hydroxyl groups in addition to epoxide groups.

While polyglycidyl ethers of polyphenol can be employed, it may bedesirable to react a portion of the reactive sites (hydroxyl or in someinstances epoxy) with a modifying material to vary the filmcharacteristics of the resin. The epoxy resin may be modified, forexample, with isocyanate group containing organic materials or otherreactive organic materials.

Other useful polyepoxides are the novolak resins including, for example,the novolak epoxy resins ECN 1235 (trademark) and ECN 1273 (trademark),Ciba-Geigy Corporation.

According to preferred embodiments of the present invention, epoxidecompounds other than diepoxide compounds provide no more than about 15%and most preferably substantially none of the total epoxidefunctionality in the reactants used to form the epoxy-ester resin.

(ii) Dicarboxylic Acid Reactant

Dicarboxylic acids suitable for chain extending diepoxides discussedabove preferably have a number average molecular weight of between about145 and about 1000 and more preferably between about 500 and about 600.Suitable dicarboxylic acids include numerous commercially availablematerials, many of which will be readily apparent to the skilled of theart in view of the present disclosure. Suitable dicarboxylic acidsinclude saturated and unsaturated, cyclic and acyclic, aliphatic andaromatic dicarboxylic acids and a compatible mixture thereof. Acyclicaliphatic dicarboxylic acids are generally preferred in view of theenhanced flexibility they provide to the cured coatings of theinvention. Preferred dicarboxylic acids have the general formula (I):

    HOOC--R"'--COOH                                            (I)

wherein R"' is a divalent linking moiety substantially unreactive withthe diepoxide resin and the acid component. It will be apparent to theskilled of the art in view of the present disclosure, that R"' should besubstantially unreactive also with the hydroxy functional secondaryamine employed in preparation of the epoxy ester resin, and with hydroxyfunctionality generated in the chain-extension reaction. Preferably R"'is a divalent, organic, linking moiety. Particularly preferred are thosedicarboxylic acids wherein R"' is selected from the group comprising astraight or branched alkylene or alkylidene moiety, preferably of about4-42 carbons, for example (CH₂)_(n) wherein n is preferably from about 4to about 42, and the like or a mixture thereof. Dicarboxylic acids ofthis character have been found to provide good reactivity with thepreferred diepoxides described above and to provide, ultimately, curedcoatings of the invention having excellent physical properties, mostnotably excellent flexibility and corrosion protection.

Exemplary dicarboxylic acids include adipic acid,3,3-dimethylpentanedioic acid, benzenedicarboxylic acid,phenylenediethanoic acid, napthalenedicarboxylic acid, pimelic acid,suberic acid, azelaic acid, sebacic acid, and the like or a compatiblemixture of any of them. The anhydrides of these acids, where theanhydrides exists, are, of course, embraced in the term "acid". Whiledicarboxylic acids according to formula (I) can be used, wherein R"' isan alkylene chain of less than 4 carbons, for example oxalic acid,malonic acid, succinic acid, glutaric acid and the like, these are lesspreferred in view of the somewhat lesser degree of flexibility providedthereby. Preferably the dicarboxylic acid provides two terminal carboxylgroups. Similarly, preferred aromatic dicarboxylic acids are thosewherein the carboxylic groups are more spaced apart, for example,1,4-benzene-dicarboxylic acid and 2,7-naphthalenedicarboxylic acid.

The most preferred dicarboxylic acids are substantially saturated,acyclic, aliphatic dimer acids, which are well known to the skilled ofthe art and readily commercially available. These are typically thedimerization reaction products of fatty acids which have from 4 to 22carbons and a terminal carboxyl group. Of these, dimer acid of 36carbons is most preferred since it provides excellent reactivity withthe preferred diepoxides described above, and provides, ultimately,cured coatings of the invention having excellent physical properties. Inaddition, dimer acid of 36 carbons is readily commercially available,for example, as Empol 1014 (trademark), Empol 1016 (trademark) and Empol1018 (trademark), each available from Emery Industries, Inc.,Cincinnati, Ohio. It should be recognized that most or all commerciallyavailable dimer acids contain some portion of trimer acid, typically,for example, about 5-10% but in some cases as much as 30% or more, andalso contain a usually smaller portion of monocarboxylic acid. As usedherein, the term "dimer acid" includes those containing such materials.Most useful in the present compositions are products that contain mostlydibasic acid and none or low amounts of tribasic and monobasic acids.

Aliphatic dicarboxylic acids are seen to provide additional advantages.In particular, while not wishing to be bound by theory, it is presentlyunderstood that epoxy ester resins derived therefrom wet the substratesurface better and provide enhanced adhesion between the substrate andthe cured coating. They also flow better and, thus, provide an excellentsmooth surface upon being cured. Also, the aliphatic units provideenhanced flexibility to the cured coating and this flexibility of thecoating is seen to provide enhanced impact resistance.

Where corrosion protection for the substrate is particularly important,it may be preferred to employ dicarboxylic acid according to formula (I)above, wherein R"' is, at least in part, aromatic. It is believed thatsuch aromatics in the coating composition of the invention, such as aprimer composition for a metal substrate, are more resistant tohydrolysis than are aliphatics and, therefore, provide enhancedcorrosion and moisture resistance. Of course, as also noted above,according to preferred embodiments of the epoxy ester resin, describedabove, the diepoxide reactant provides aromatic units to the resin andthis would similarly contribute to corrosion and moisture resistance.

Other suitable dicarboxylic acids for the epoxy ester resin of thepresent invention will be apparent to the skilled of the art in view ofthe present disclosure.

(iii) Acid Component Reactant

Numerous suitable primary hydroxy functional acids will be apparent tothe skilled of the art in view of the present disclosure, including manywhich are readily commercially available. These include C₃ -C₂₆ hydroxyfunctional acids, wherein the acid contains one carboxyl group and oneor more hydroxyl groups and no other functional groups which wouldsubstantially interfere with the chain-extension reaction, i.e., whichwould be substantially unreactive with the chain-extension reactantsdescribed above and with the diepoxide chain-extension reaction productif the hydroxy acid is to be added subsequently. The preferred hydroxyfunctional acids correspond to the general chemical formula: ##STR1##wherein R₁, R₂, R₃ and R₄ are the same or different and each preferablyis lower alkylene such as methylene and ethylene and Z and Z' areselected independently from hydrogen, hydroxyl, and any othernon-interfering functionality such as nitrile ester group, halogen,amide, etc. Suitable hydroxy acids which may be employed in the chainterminating reaction include, but are not limited to, dimethylolpropionic acid which is most preferred, bis(hydroxy ethyl)propionicacid, bis(hydroxy propyl)propionic acid, and the like and a compatiblemixture of any of them. Preferably, the hydroxy acid contains two ormore hydroxyl groups, i.e., at least one of Z and Z' contains a hydroxylgroup.

Optionally, the acid component may further comprise fatty acid. Suitablefatty acids include numerous commercially available fatty acids such as,for example, those derived from or contained in either animal orvegetable fat or oil. Preferred are fatty acids from about 8 to about 18carbons since these are found to provide flexibility to the curedcoating. Also preferred among the fatty acids are the more saturatedfatty acids, since it appears that olefinic unsaturation in the fattyacid can undergo a polymerization-type reaction between such doublebonds during the synthesis of the epoxy ester resin of the invention.Unsaturated fatty acids are suitable for use, however, such as, forexample, oleic acid, linoleic, linolenic or the like and mixtures ofthose acids, and can be used together with a suitable inhibitor for thepolymerization-type reaction such as hydroquinone or the like, of whichmany are commercially available and will be apparent to the skilled ofthe art in view of the present disclosure. In addition, aromatic fattyacids are commercially available and can be employed. Preferred for useare the substantially saturated fatty acids such as Soya fatty acidwhich is most preferred, and butyric, lauric, palmitic and stearic fattyacids and the like or a compatible mixture of any of them. These arerelatively inexpensive and have been found to provide good reactivitywith the preferred diepoxides described above. For convenience of use,the fatty acids which are semisolid or liquid at room temperature aregenerally preferred over the solid fatty acids.

The hydroxy functional epoxy ester resin used in the composition of thepresent invention can be made according to techniques well known to theskilled of the art. The chain termination reaction occurs eithersimultaneously with the chain extension of the diepoxide withdicarboxylic acid or occurs subsequent thereto. If the reactions arecarried out sequentially, diepoxide and dicarboxylic acid are chargedinto a suitable reactor and heated. The reactants are used in relativeproportions to yield a chain extension reaction product bearing twounreacted epoxy groups and preferably substantially no unreactedcarboxyl functionality. Suitable separation techniques are known to theskilled of the art for removal of unused reactants. It should berecognized that to assure rapid and/or more complete reaction of thediepoxide with carboxyl functionality, it is usually preferred to have acatalyst present. The use of catalyst is found to provide epoxy esterresin which yields coating compositions of advantageous physicalproperties. Suitable catalysts are commercially available and includeany of the well known catalysts for epoxy-carboxy reactions such as, forexample, lithium neodecananoate which is preferred, and sodiumcarbonate, tertiary amines and other organometallic catalysts. Othersuitable catalysts will be apparent to the skilled of the art in view ofthe present disclosure. After completion of the chain extension reactionof diepoxide with dicarboxylic acid, the diepoxide reaction product isreacted with the acid component in chain terminating reaction inapproximately 1 to 1 equivalent ratio. This ratio is preferred sinceexcess epoxy could result in gelation of the reaction mixture.

If the reactions are carried out simultaneously, the reactants are usedin amounts suitable to yield the desired reaction ratio in view of therelative reactivity of the dicarboxylic acid and the hydroxy functionalacid, and in view of the desired molecular weight range for the reactionproduct.

B. Crosslinking Agent

The crosslinking agent employed in the novel solvent based coatingcompositions of the invention comprises polyfunctional, hydroxy-reactivecrosslinking agent selected, preferably, from aminoplast crosslinkingagents and blocked polyisocyanate crosslinking agents.

(a) Blocked Polyisocyanate Crosslinking Agent

These embodiments of the novel solvent based coating compositions of theinvention employing blocked polyisocyanate crosslinking agents exhibitexceptional shelf stability even when corrosion inhibiting pigments suchas zinc chromate are used in high concentrations.

As used herein "blocked polyisocyanate" means an isocyanate compoundcontaining two or more isocyanato groups, each of which has been reactedwith a blocking agent which will prevent reaction of the isocyanategroup at room temperature with compounds that conventionally react withsuch groups, and at least some of which will permit that reaction tooccur at higher (cure) temperatures. In general, the blockedpolyisocyanate may be prepared by reacting a sufficient quantity of anactive hydrogen containing blocking agent with the polyisocyanate toinsure that substantially no free isocyanato groups are present. Theblocking agent may be represented by the formula BH and may be selectedfrom numerous materials, hereinafter discussed, which bear an activehydrogen.

The proper proportion of blocked polyisocyanate crosslinking agent tohydroxy functional epoxy ester resin will depend, in part, upon theproperties desired in the coating to be produced and, in part, upon thedesired cure response of the coating composition (which will depend, inturn, upon the baking schedule to be used in curing the coatingcomposition) and, in part, upon the desired storage stability of thecomposition, that is, upon the desired shelf life. Accordingly, theamounts of crosslinker that can be used with the epoxy ester resinvaries considerably. Preferably the blocked polyisocyanate crosslinkingagent is included in compositions of the invention in amounts such thatupon deblocking of the blocked isocyanato groups at the cure temperatureof the composition, the crosslinking agent will provide between about0.5 and about 1.6, preferably between about 0.8 and about 1.3, reactiveisocyanato groups per reactive group on the film forming resin of thecoating composition as described above. Blocked polyisocyanates ofnumerous types may be employed in the compositions of the invention.Particularly suitable blocked polyisocyanates, which will be discussedfurther hereinafter, include blocked polymethylene polyphenolisocyanates, isocyanurate ring containing blocked polyisocyanates andcertain oligoester modified blocked polyisocyanates.

In the preparation of the blocked polyisocyanate crosslinking agent, anysuitable organic polyisocyanate may be used. Representative examplesinclude the aliphatic compounds such as trimethylene, tetramethylene,pentamethylene, hexamethylene, 1,2-propylene, 1,2-butylene,2,3-butylene, 1,3-butylene, ethylidene and butylidene diisocyanates; thecycloalkylene compounds such as 1,3-cyclopentane, 1,4-cyclohexane, and1,2-cyclohexane diisocyanates; the aromatic compounds such asm-phenylene, p-phenylene, 4,4'-diphenyl, 1,5-naphthalene, and1,4-naphthalene diisocyanates, the aliphatic-aromatic compounds such as4,4'-diphenylene methane, 2,4- or 2,6-tolylene, or mixtures thereof,4,4'-toluidine, and 1,4-xylylene diisocyanates; substituted aromaticcompounds such as dianisidine diisocyanate, 4,4'-diphenyletherdiisocyanate and chlorodiphenylene diisocyanate; the triisocyanates suchas triphenyl methane-4,4',4"-triisocyanate, 1,3,5-triisocyanate benzeneand 2,4,6-triisocyanate toluene; the tetraisocyanates such as4,4'-diphenyl-dimethyl methane-2,2',5,5'-tetraisocyanate; and thepolymerized polyisocyanates such as tolylene diisocyanate dimers andtrimers, and the like.

In addition, the organic polyisocyanate may be a prepolymer derived froma polyol including polyether polyol or polyester polyol, includingpolyethers which are reacted with excess polyisocyanates to formisocyanate-terminated prepolymers. The polyols may be simple polyolssuch as glycols, e.g., ethylene glycol and propylene glycol, as well asother polyols such as glycerol; tri-methylolpropane, pentaerythritol,and the like, as well as mono-ethers such as diethylene glycol,tripropylene glycol and the like and polyethers, i.e., alkylene oxidecondensates of the above. Among the alkylene oxides that may becondensed with these polyols to form polyethers are ethylene oxide,propylene oxide, butylene oxide, styrene oxide and the like. These aregenerally called hydroxyl-terminated polyethers and can be linear orbranched. Examples of polyethers include polyoxyethylene glycol,polyoxypropylene glycol, polyoxytetramethylene glycol,polyoxyhexamethylene glycol, polyoxynonamethylene glycol,polyoxydecamethylene glycol, polyoxydodecamethylene glycol and mixturesthereof. Other types of polyoxyalkylene glycol ethers can be used.Especially useful polyether polyols are those derived from reactingpolyols such as ethylene glycol, diethylene glycol, triethylene glycol,1,4-butylene glycol, 1,3-butylene glycol, 1,6-hexanediol, and theirmixtures; glycerol, trimethylolethane, trimethylolpropane,1,2,6-hexanetriol, pentaerythritol, dipentaerythritol,tripentaerythritol, polypentaerythritol, sorbitol, methyl glucosides,sucrose and the like with alkylene oxides such as ethylene oxide,propylene oxide, their mixtures, and the like.

A particular class of aromatic polyisocyanates which may be employed inthe novel solvent based coating compositions of the invention arepolymethylene polyphenol isocyanates having the formula: ##STR2##wherein x equals 1 to 3. The compounds, sold under the tradename "PAPI"by the Upjohn Chemical Company of Kalamazoo, Mich., are particularlyuseful in compositions of the invention, resulting in compositionsexhibiting desirable toughness in the final cured coating.

The active hydrogen containing blocking agents which are reacted withthe above described organic diisocyanates may be selected from numerousblocking agents which will be apparent to those skilled in this art.Preferred blocking agents include, for example, those selected from thegroup consisting of (i) aliphatic, cycloaliphatic and aromatic alkylmonoalcohols; (ii) hydroxyl amines; (iii) oximes; (iv) lactams; and (v)triazoles. Any suitable aliphatic, cycloaliphatic or aromatic alkylmonoalcohol may be used as a blocking agent in accordance with thepresent invention. For example, aliphatic alcohols, such as methyl,ethyl, chloroethyl, propyl, butyl, amyl, hexyl, heptyl, octyl, nonyl,3,3,5-trimethylhexyl, decyl, and lauryl alcohols, and the like may beemployed. Suitable cycloaliphatic alcohols include, for example,cyclopentanol, cyclohexanol and the like, while aromatic-alkyl alcoholsinclude phenylcarbinol, methylphenylcarbinol, and the like. Minoramounts of even higher molecular weight relatively non-volatilemonoalcohols may be used, if desired, to serve as plasticizers in thecoatings provided by the invention. Examples of hydroxyl amines whichmay be employed as blocking agents include ethanol amine and propanolamine. Suitable oxime blocking agents include, for example,methylethylketone oxime, acetone oxime and cyclohexanone oxime. Examplesof lactams which may be used as blocking agents are ε-caprolactam,γ-butyrolactam and pyrrolidone, while suitable triazoles includecompounds such as 1,2,4-triazole, 1,2,3-benzotriazole, 1,2,3-tolyltriazole and 4,5-diphenyl-1,2,3-triazole. Particularly preferred activehydrogen containing blocking agents are methylethyl ketoxime and2-ethylhexanol.

(i) Isocyanurate Ring Containing Blocked Isocyanate Compounds

Within the scope of the above general class of blocked polyisocyanatecrosslinking agents, a particular class or type of blockedpolyisocyanate crosslinking agent which may be employed in the novelsolvent based coating compositions of the invention comprisesisocyanurate ring containing blocked isocyanate compounds. In general,these blocked polyisocyanates may be formed by blocking with theaforementioned blocking agents. These compounds may be formed bycyclotrimerization of difunctional isocyanates. Usually, the reactiondoes not stop in this stage and continues through the formation ofpolyfunctional oligomers or a mixture of such oligomers with a portionof the pure trifunctional polyisocyanate. Mixtures of trifunctionalproduct and various polyfunctional oligomers are commercially available.

A particularly desirable blocked polyisocyanate crosslinking agent isthe blocked form of the pure trifunctional isocyanurate represented bythe following formula: ##STR3## wherein each L is selected independentlyfrom the group consisting of aliphatic, cycloaliphatic and aromaticgroups and combinations thereof and B is the residue of an activehydrogen containing blocking agent. More specifically, this compound isdisclosed in United States patent application Ser. No. 368,178 filedApr. 14, 1982, the disclosure of which is hereby incorporated byreference.

(ii) Oligoester Modified Blocked Polyisocyanates

Still further particular blocked polyisocyanates useful as crosslinkingagents in the noval solvent based coating compositions of this inventionare oligoester modified blocked polyisocyanates prepared from aparticular class of oligoester diols and triols. A first type of sucholigoester modified blocked polyisocyanate is prepared from organicdiisocyanates wherein one isocyanato group is more reactive than theother, with the more reactive isocyanato first being blocked with ablocking agent and the remaining isocyanato group then being reactedwith hydroxyl functionality of an oligoester diol or triol as referredto above. The second type of oligoester modified blocked polyisocyanatemay be prepared by reacting oligoester diols from the aforementionedclass of oligoesters with an excess of organic diisocyanate so as toform an isocyanato terminated prepolymer followed by blocking of theterminal isocyanato groups of the prepolymer with an active hydrogencontaining blocking agent. Each of these materials is particularlyuseful in the compositions of the invention and produces final curedcoating compositions exhibiting outstanding flexibility.

Oligoesters of the type employed in the preparation of thesecrosslinking agents are described in U.S. Pat. No. 4,322,508 issued Mar.30, 1982, the disclosure of which is hereby incorporated by reference.The hydroxy functional oligoesters within the useful class of materials(i) have a number average molecular weight (Mn) between about 150 andabout 3000, preferably between about 230 and about 1000, (ii) bear 2 or3 hydroxyl groups per molecule, and (iii) are formed by anesterification reaction between a carboxylic acid and an epoxide. Theesterification reaction products are selected from the group consistingof:

(a) the esterification reaction product of polycarboxylic acid, i.e.,carboxylic acid bearing 2 or more carboxyl groups, and monoepoxide;

(b) the esterification reaction product of polyepoxide, i.e., a compoundhaving 2 or more epoxide groups, and monocarboxylic acid, preferablycontaining no ethylenic unsaturation, and bearing no hydroxyfunctionality;

(c) the esterification reaction product of hydroxy functional carboxylicacid and mono- or polyepoxide, preferably monoepoxide;

(d) the esterification reaction product of monocarboxylic acid andhydroxy functional mono- or polyepoxide, preferably monoepoxide; and

(e) mixtures of (a)-(d).

As noted above, the first type of oligoester modified blockedpolyisocyanate crosslinking agent is prepared by (i) reacting organicdiisocyanate bearing one isocyanato group which is more reactive thanthe other with a sufficient amount of an active hydrogen containingblocking agent to react substantially with all of the more reactiveisocyanate groups, thus providing a half-blocked diisocyanate and (ii)reacting this half-blocked intermediate with the above discussedoligoester. The organic diisocyanates employed in this synthesis, aswell as the active hydrogen containing blocking agents, are discussedabove in connection with the preparation of the isocyanurate ringcontaining blocked isocyanate crosslinking agents useful in compositionsof the invention. The organic polyisocyanate-blocking agent adductintermediate is formed by reacting a sufficient quantity of the blockingagent with the organic diisocyanate to insure that one of the two --NCOgroups on the diisocyanate is reacted. The reaction between the organicdiisocyanate and the blocking agent is exothermic and the diisocyanateand the blocking agent are preferably admixed at temperatures no higherthan about 80° C., preferably below about 50° C., to minimize theexothermic effect.

The diisocyanate blocking agent intermediate is next reacted with theoligoester diol or triol described above so as to react substantiallyall free or unblocked isocyanato groups of the intermediate withhydroxyl groups of the oligoester. This reaction is carried outdesirably at a temperature of about 80°-120° C.

As also discussed above, the second type of oligoester modified blockedpolyisocyanate crosslinking agent useful in the novel solvent basedcoating compositions of the invention is prepared by reacting an excessof organic diisocyanate with an oligoester diol from the above describedclass of oligoesters followed by reaction of the terminal isocyanatogroups formed on the resultant prepolymer with an active hydrogencontaining blocking agent as described above so as to react withsubstantially all the isocyanato groups. The diisocyanate startingmaterial is used in excess in amounts sufficient to insure that theintermediate is isocyanate terminated. Therefore, it is preferable thatthe organic diisocyanates and the dihydroxy functional oligoester bereacted in a molar ratio of from greater than 1:1 up to 2:1. Numerousdiisocyanates of the type described hereinbefore may be employed in thepreparation of this intermediate. While it is not necessary that oneisocyanato group be more reactive than the other, the preparation ofthis type of crosslinking agent does not preclude the use of suchmaterial.

(b) Aminoplast Crosslinking Agent

According to alternative embodiments of the invention, the novel solventbased coating compositions employ hydroxy-reactive polyfunctionalaminoplast crosslinking agents. It will be recognized that compatiblecombinations of suitable polyfunctional aminoplast crosslinking agent(s)and blocked polyisocyanate crosslinking agent(s) also can be used.Included within the aminoplast crosslinking agents suitable for use inthe coating composition are numerous materials which are well known tothe skilled of the art including, for example, alkylated melamineformaldehyde resins with one to about eight carbon atoms in the alkylmoiety. Other suitable aminoplast crosslinking agents will be apparentto the skilled of the art in view of the present disclosure. Many suchcrosslinking agents are readily commercially available including, forexample, the Resimene (trademark) series, Monsanto Company, St. Louis,Mo., the most preferred being Resimene 717 (trademark), described as alow temperature cure methylated melamine-formaldehyde resin.

In addition, suitable polyfunctional aminoplast crosslinking agents canbe prepared employing conventional techniques. Accordingly, for example,a lower alkanol such as methanol, ethanol, butanol, isobutanol,isopropanol, hexanol, 2-ethylhexanol or the like or a mixture of any ofthem is reacted with a melamine formaldehyde. Preferred crosslinkingagents of this type include butylated melamine formaldehyde resin,methylated/butylated formaldehyde resin and polyalkyl hexamethoxymethylmelamine resin which is most preferred in view of its relatively lowercost, ready commercial availability, and its low reactivity with thehydroxy functional epoxy ester resin of the invention at non-elevatedcure temperatures. In this regard, preferred polyfunctional aminoplastcrosslinking agent is substantially unreactive with the epoxy esterresin at or below about 60° C. Other suitable aminoplast crosslinkingagents will be apparent to the skilled of the art in view of the presentdisclosure.

The proper proportion of polyfunctional aminoplast crosslinking agent toepoxy ester resin will depend, in part, upon the properties desired inthe coating to be produced and, in part, upon the desired cure responseof the coating composition (which will depend, in turn, upon the bakingschedule intended for curing the coating composition) and, in part, uponthe desired storage stability of the coating composition, that is, uponthe desired shelf life. Accordingly, the amounts of epoxy ester resinthat can be blended with the crosslinker to form coating compositions ofthe invention may be varied considerably. Preferably, the crosslinkingagent is used in amounts of about 5% to about 40% by weight of the totalresin solids, more preferably about 20% to about 30%.

C. General Discussion--Other Aspects of the Invention and OtherComponents

The coating compositions of the invention provide a cured coating havingthe advantageous physical properties described above, over a wide rangeof cure temperatures and a wide range of solids levels. Morespecifically, the coating compositions according to preferredembodiments of the invention cure at temperatures from as low as about120° C. or less within about 15 minutes or less, and yet to cure andsuffer no significant loss of advantageous physical properties attemperatures as high as about 200° C. or more for periods up to about 60minutes or more. Considered together with the good storage stability ofthe coating composition, it can be readily recognized that the presentinvention provides a significant advance in the coating composition art.

It will be within the skill of the art to determine the proper volatileorganic content for a given coating composition of the invention and fora given application. Preferred solvents have relatively low volatilityat temperatures appreciably below their boiling points such that solventevaporation is low during storage and during application of the coatingcomposition to the substrate. A suitable solvent system may include, forexample, toluene, methyl ethyl ketone, isobutyl acetate, xylene,cellosolve acetate, acetone and a mixture of any of them. Other solventswhich may be employed include terpenes, aliphatic and aromatic naphthas,and the like. Additional suitable solvents are commercially availableand will be apparent to the skilled of the art in view of the presentdisclosure. Where the composition is to be formulated as a higher solidscontent primer composition employing aminoplast crosslinking agent, itgenerally is preferred to employ a portion of C-1 to C-8 alcohol solventsuch as, for example, butanol, pentanol, hexanol, and the like or amixture of any of them since these inhibit the crosslinking reaction ofthe polyfunctional aminoplast resin with the epoxy ester resin at roomtemperature and thereby improve storage stability. At elevatedtemperature during cure, the alcohol solvent evaporates and, hence,ceases to inhibit the crosslinking reaction. Preferred solvents alsoinclude, for example, methyl amyl ketone and the like, or a mixturethereof with C-1 to C-8 alcohol such as, for example, a 1:2 mixture byweight of butanol and methyl amyl ketone, respectively.

Any solvent allowed to remain in the cured coating should be inert so asto avoid adverse effect upon the cured coating or upon another coatinglayer used in conjunction with it during the curing process orthereafter. Preferrably, the cured coating is substantially free ofsolvent.

Sufficient solvent is used to reduce the viscosity of the coatingcomposition to a level suitable for application to the substrate in thedesired manner. It can be applied by any conventional method, includingbrushing, dipping, flow coating, spraying, etc. Spraying will generallybe preferred, for example, for applying the compositions as anautomotive primer.

Also preferably included in compositions of the invention employingaminoplast crosslinking agent is any of a variety of acid catalyst knownto the skilled of the art to catalyse the aminoplast crosslinkingreaction, for example, p-toluenesulfonic acid, phosphoric acid, phenylacid phosphate, butyl phosphate, butyl maleate, and the like or acompatible mixture of any of them. Such acid catalyst is most useful forcoating compositions intended for low temperature curing schedulesand/or when highly etherified melamine resins are used such ashexa(methoxymethyl)melamine or the like. Such catalysts are used inamounts which depend, in part, upon the intended baking (curing)schedule. Typically, amounts of about 0.2% to about 3.% are used, morepreferably about 0.4% to about 0.6% by weight of total resin solids. Inaddition to catalyst, flow control agent(s), for example, polybutylacrylate; wetting agent(s), for example, silicone; pigments; pigmentdispersants; corrosion inhibitors, for example, chromate pigments,numerous of all of which are known to the skilled of the art, may beemployed in the coating compositions of the invention. In addition,suitable reactive additives can be used, including, for example, lowmolecular weight diol flow control agents and reactive diluents.

Compositions of the invention, and in particular primers of highersolids content, also may include antisettling or anti-sagging agents tocontrol the thixotropic properties of the composition. Exemplary ofavailable materials suitable for this purpose are Dislon (trademark)6900-20X manufactured by Kusumoto Chemicals, Ltd., Tokyo, Japan and soldby King Industries, Norwalk, CT 06852; Bentone (trademark), 38, N. L.Industries, Highstown, N.J.; and Cab-O-Sil (trademark) M-5, CabotCorporation.

Curing the coating composition requires baking for sufficient time atsufficiently elevated temperature to react the crosslinking agent withthe hydroxy functionality of the epoxy ester resin. The time andtemperature required to cure the coating are interrelated and dependupon the particular epoxy ester resin, crosslinking agent, solvent andother materials, if any, and the amount of each comprising the coatingcomposition. The coating composition according to preferred embodimentsof the invention, as described above, are found to provide best coatingresults when cured at temperature at about 300° F. for about 20 minutes.It is a highly significant advantage of the invention, however, thatthese same coating compositions can withstand, for example, temperatureas high as about 200° C. (390° F.) for periods of time as long as about60 minutes. Accordingly, great flexibility is provided in both designingand implementing a curing schedule for parts coated with the coatingcompositions of the invention. Thus, in the assembly of automotivevehicles, for example, vehicles unavoidably held in a curing oven forlong periods of time during unplanned assembly line shut-downs arerecovered with cured and unharmed coatings.

Coating compositions according to the present invention, comprising thenovel crosslinkable hydroxy functional epoxy ester resin of theinvention and blocked polyisocyanate crosslinking agent, especially thepreferred materials described above, are found to afford cured coatingswith improved corrosion resistance, thus representing a significantadvance in the art. A most preferred use of the coating composition ofthe invention is as a sprayable primer for use on a bare metal substratesuch as a household or industrial appliance housing or an automotivevehicle body. Primer compositions typically are pigmented and anypigments commonly included in primer compositions for metal substratesand acrylic dispersion topcoats such as, for example, carbon black, ironoxide, lithopone, magnesium, silicate, silica, barium sulfate, TiO₂,chrome yellow, calcium chromate, strontium chromate, zinc potassiumchromate any the like may be used. The primer can be pigmented accordingto known methods including, for example, by grinding pigments in aportion of the curable resin and adding to the primer composition. Thepigment-to-binder ratio of the primer may be as much as 4:1 by weight,respectively. It is preferred, however, to use a primer having apigment-to-binder ratio of about 1:1 to 2:1 by weight, respectively.

No special expedients are necessary in formulating the primercompositions of this invention. For example, they may be prepared simplyby incorporating the resinous components in a suitable solvent system.Thus, for example, by suitable mixing or agitation, each resinouscomponent may be dissolved in a solvent and the resulting solutionscombined to form finished primer compositions.

The solvent system may be any suitable combination of organic solventsas described above. For a sprayable automotive vehicle primer thesolvent will comprise preferably about 25 to about 35 percent by weightof the total coating compositions although, of course, larger or smalleramounts may be utilized depending upon the solids content desired.

The primer is generally thinned to from about 65 to about 70 percentsolids content for spraying purposes with conventional thinners such asaromatic hydrocarbons, commercial petroleum cuts which are essentiallyaromatic, and the like, and sprayed on to the metal base and cured. Theprimer is cured at elevated temperatures by any convenient means such asbaking ovens or banks or infra-red heat lamps. Curing temperatures arepreferably from about 135° C. to about 165° C. although curingtemperatures from about 100° C. to about 230° C. may be employed, ifdesired.

The invention will be further understood by referring to the followingdetailed examples. It should be understood that the specific examplesare presented by way of illustration and not by way of limitation.Unless otherwise specified, all references to "parts" are intended tomean parts by weight.

EXAMPLE I

Into a suitable reactor the following materials are charged:

1240 parts--Epon 829

1300 parts--Epon 1016

840 parts--Soya Fatty Acid

268 parts--Dimethylolpropionic Acid

33 parts--Lithium Neodecanoate (catalyst)

The mixture is heated to 350° F. After four hours the acid number ismeasured to be 27. At this point Cardura E Ester, 401 parts, is addedand the mixture heated at 350° F. for one hour. The acid number is thenmeasured to be 1.9. The mixture is cooled and 754 parts of Methyl AmylKetone are added. The final resin has a Gardner-Holt viscosity of Z-2 at81% solids.

EXAMPLES II-V

Epoxy ester resins according to the invention are prepared in the mannerdescribed below. The components employed are shown in Table I. Thediepoxide, and dimer acid, hydroxy functional acid, fatty acid, if any,and catalyst, if any, are charged in a suitable reactor. The mixture isheated up to about 177° C. (350° F.). At this point, exothermic reactiontakes place that brings the temperature up to about 188°-199° C.(370°-390° F.). The reaction is continued at this temperature until theacid number drops below 6. Then the product is cooled down to about 121°C. (250° F.) and thinned to 80% non-volatiles by weight with methyl amylketone. In Table I, all amounts are shown in parts by weight.

                  TABLE I                                                         ______________________________________                                                       Example                                                                       II   III      IV     V                                         ______________________________________                                        Epon 829.sup.1   500    500                                                   DER 333.sup.2                    500                                          Araldide RD-2                         622                                     Empol 1016       309    309      309  564                                     Dimethylol Propanic Acid                                                                       190     95      190  174                                     Soya Fatty Acid         200           364                                     Sodium Carbonate                      0.5                                     Methyl Amyl Ketone                                                                             250    276      250  431                                     Lithium Neodecanoate                                                                            6      6        6    6                                      % Non Volatiles  80.0   79.9     79.6 79.8                                    Viscosity        Z.sub.2                                                                              Z        Z.sub.2                                                                            V                                       Acid Number       5.2    4.8      6.1 6.8                                     ______________________________________                                         .sup.1 Trademark, Shell Chemical Co. (diepoxide; specifically, bisphenolA     epichlorohydrin epoxy resin)                                                  .sup.2 Trademark, Dow Chemical Co. (diepoxide)                           

EXAMPLE VI

A millbase, that is, a composition pigment paste is prepared by grindingin a ballmill the following mixture:

    ______________________________________                                        Composition        Parts                                                      ______________________________________                                        Barium Sulfate     1626                                                       Red Iron Oxide     60                                                         Titanium dioxide   105                                                        Silica             75                                                         Strontium chromate 99                                                         Polyethylene Wax   48                                                         Xylene             200                                                        Toluene            240                                                        Methyl Ethyl Ketoxime                                                                            57                                                         Resin of Example I 264                                                        ______________________________________                                    

EXAMPLES VII-X

Coating compositions according to the invention are prepared, each beingadapted for use as a high solids, sprayable, pigmented primer forapplication over bare, unpolished steel automotive vehicle body panelsin an automobile vehicle assembly operation. The coating compositioncomponents are shown in Table II, below. Each coating composition isreduced with methyl amyl ketone to about 18-25 sec. #4 Ford Cup, 27° C.(80° F.) to provide a preferred spraying viscosity. It will be notedthat use of a drier, as in Examples VII, VIII and IX, is optional, tocatalyse reaction of fatty acid double bonds to provide additionalcrosslinking in the cured resin. In Table II, all amounts are expressedin parts by weight.

                  TABLE II                                                        ______________________________________                                                       Example                                                                       VII   VIII    IX      X                                        ______________________________________                                        Epoxy Ester Resin                                                                              270     270     270   270                                    of Example I                                                                  Phenyl acid phosphate                                                                          --       1      --    --                                     PTSA             --      --       1     1                                     Millbase of Example VI                                                                         800     800     800   800                                    Resimine 717.sup.1                                                                             110     110     --    --                                     Cymel 325.sup.2  --      --      110   --                                     Cymel 303.sup.3  --      --      --     93                                    6% Manganese Naphthanate                                                                        4       4       4    --                                     (Drier)                                                                       Butanol           35      35      35   --                                     ______________________________________                                         .sup.1 Trademark, Monsanto Co., St. Louis, MO (low temperature, high          solids methylated melamineformaldehyde resin crosslinking agent).             .sup.2 Trademark, American Cyanamid, Wayne, New Jersey, (highly methylate     melamine formaldehyde resin).                                                 .sup.3 Trademark, American Cyanamid, Wayne, New Jersey,                       (hexa(methoxymethyl)melamine).                                           

EXAMPLES XI-XIV

Coating compositions according to the invention, each adapted for use asa sprayable pigmented primer for application over, for example, bare,unpolished steel automotive vehicle body panels in an automotive vehicleassembly operation, are prepared as shown in Table III, below. It shouldbe noted that use of a drier, as in the coating copositions illustratedin Table III, is optional. The epoxy ester resin employed in eachcoating composition is identified by reference to the Example accordingto which it was prepared. All amounts are expressed in parts by weight.

                  TABLE III                                                       ______________________________________                                                   Example                                                                       XI     XII      XIII     XIV                                                  Exp. II                                                                              Exp. III Exp. IV  Exp. V                                    ______________________________________                                        Epoxy Ester Resin                                                                          270      270      270    270                                     Phenyl acid phosphate                                                                       1        1        1      1                                      Millbase of Exp. VI                                                                        800      800      800    800                                     Resimine 717.sup.1                                                                         110      110      110    110                                     6% Manganese           4               4                                      Naphthanate (Drier)                                                           Butanol       35       35       35     35                                     ______________________________________                                         .sup.1 Trademark, Monsanto Co., St. Louis, MO (low temperature, high          solids methylate melamineformaldehyde resin crosslinking agent).         

EXAMPLE XV

A blocked isocyanate crosslinker useful in compositions of the inventionis prepared. In a suitable reactor, 417 parts of PAPI 580 (trademark,The Upjohn Company, Kalamazoo, Mich.) are charged under a nitrogenblanket. 261 parts of methyl amyl ketoxime are added dropwise in aperiod of 30 minutes keeping the temperature below 210° F. by externalcooling. After the addition is completed the temperature is maintainedat 210° F. for an additional hour at which time the complete reaction ofthe isocyanate is verified by I.R. The batch is then thinned with 226parts of methyl amyl ketone. The resulting resin has a viscosity of Z₆₊at 75% solids.

EXAMPLES XVI-XX

Blocked isocyanate crosslinking agents useful in compositions of theinvention are prepared in the manner generally described in Example XVfrom the components shown in Table IV.

                  TABLE IV                                                        ______________________________________                                                     Example                                                                       XVI  XVII      XVII    XIX                                       ______________________________________                                        Dezmodur L-2291A.sup.1                                                                       360    360                                                     PAPI - 27.sup.2                 399                                           Dezmodur IL.sup.3                     525                                     Methyl amyl ketoxime                                                                         174              261   87                                      Benzotriazole         238                                                     Methyl amyl ketone                                                                           133    150       220                                           % Non-Volatiles                                                                              80.0   80.1      75.1  57                                      Viscosity      Z.sub.11/2                                                                           Z.sub.7   Z.sub.2                                                                             Z                                       ______________________________________                                         .sup.1 Trademark, Mobay Chemical Corporation (Pittsburgh, Pennsylvania)       .sup.2 Trademark, The Upjohn Company (Kalamazoo, Michigan)                    .sup.3 Trademark, Mobay Chemical Corporation (Pittsburgh, Pennsylvania)  

EXAMPLES XX-XXIV

Coating compositions according to the invention are prepared, each beingadapted for use as a sprayable, pigmented primer for application overbare, unpolished steel automotive vehicle assembly operation. Thecoating composition components are shown in Table V below. Each coatingcomposition is reduced with methyl amyl ketone to about 18-25 sec. #4Ford Cup, 27° (80° F.) to provide a preferred spraying viscosity. Itwill be noted that use of a drier is optional, to catalyse reaction offatty acid double bonds to provide additional crosslinking in the curedresin. In Table V, all amounts are expressed in parts by weight.

                  TABLE V                                                         ______________________________________                                                     Example                                                                       XX   XXI    XXII    XXIII XXIV                                   ______________________________________                                        Epoxy Ester Resin of                                                                         270    270    270   270   270                                  Example I                                                                     Millbase of Example VI                                                                       800    800    800   800   800                                  Crosslinker of Example                                                                       125                                                            XV                                                                            Crosslinker of Example                                                                              115                                                     XVI                                                                           Crosslinker of Example       115                                              XVII                                                                          Crosslinker of Example             125                                        XVIII                                                                         Crosslinker of Example                   162                                  XIX                                                                           6% Manganese Naphthan-                                                                        4                                                             ate (drier)                                                                   dibutyl tin dilaruate                                                                         1      1      1     1                                         N--mehtyl pyrolidone                                                                          20     20     20    20    20                                  ______________________________________                                    

In view of the foregoing disclosure, many modifications of thisinvention will be apparent to those skilled in the art. All suchapparent modifications fall within the scope of this invention and areintended to be included within the terms of the appended claims.

INDUSTRIAL APPLICABILITY

It will be apparent from the foregoing that this invention hasindustrial applicability as a coating composition, especially as acoating composition for automotive vehicles, household appliances andthe like, and other applications where excellent humidity and solventresistance are needed to provide protection for a substrate, for examplea metal substrate, against corrosion, wear and the like.

What is claimed is:
 1. An organic solvent based thermosettingcomposition comprising:(A) crosslinkable hydroxy functional epoxy esterresin having a number average molecular weight (Mn) between about 1,000and about 5,000, said resin comprising the reaction product of diepoxidechain extended with dicarboxylic acid and chain terminated with acidcomponent comprising hydroxy functional acid; and (B) polyfunctional,hydroxy-reactive crosslinking agent selected from aminoplastcrosslinking agent, blocked polyisocyanate crosslinking agent comprisingat least two isocyanate groups blocked by reaction with an activehydrogen bearing blocking agent, and a compatible mixture of any ofthem, said crosslinking agent being included in an amount such that atthe cure temperature of the composition said cross-linking agent willprovide between about 0.5 and about 1.6 hydroxy reactive groups perhydroxy group contributed by said epoxy ester resin.
 2. The solventbased, thermosetting composition in accordance with claim 1, whereinsaid hydroxy functional epoxy ester resin comprises the reaction productof said acid component with diepoxide previously chain extended withdicarboxylic acid.
 3. The solvent based, thermosetting composition inaccordance with claim 1, wherein said hydroxy functional epoxy esterresin comprises the reaction product of diepoxide substantiallysimultaneously with dicarboxylic acid and said acid component.
 4. Asolvent based, thermosetting composition in accordance with claim 1,wherein said diepoxide is selected from the group consisting ofbisphenol-A epichlorohydrin epoxy resin, hydantoin epoxy resin, cyclicand acyclic aliphatic diepoxides, and a compatible mixture of any ofthem.
 5. A solvent based thermosetting composition in accordance withclaim 1, wherein said dicarboxylic acid is selected from the groupconsisting of saturated or unsaturated, cyclic or acyclic, aliphatic oraromatic dicarboxylic acids and mixtures thereof.
 6. A solvent basedthermosetting composition in accordance with claim 5, wherein saiddicarboxylic acid is of the general formula:

    HOOC--R"'--COOH

wherein R"' is a divalent linking moiety substantially unreactive withsaid diepoxide.
 7. A solvent based thermosetting composition inaccordance with claim 6, wherein R"' is selected from the groupconsisting of straight and branched alkylene or alkylidene moieties ofabout 4 to about 42 carbons and the like.
 8. A solvent basedthermosetting composition in accordance with claim 1, wherein saiddicarboxylic acid is selected from the group consisting of substantiallysaturated, acyclic, aliphatic dimer acids of about 4-42 carbons andmixtures thereof.
 9. The solvent based thermosetting composition ofclaim 1, wherein said primary hydroxy functional acid is selected fromC₃ -C₂₆ acids bearing a single carboxyl group, at least one primaryhydroxyl group, and no additional functionality which would reactsubstantially with said chain extension reactants or reaction productthereof.
 10. The solvent based thermosetting composition of claim 1,wherein said primary hydroxy functional acid is selected from those ofthe general formula: ##STR4## wherein n is 0 to 20; R₁, R₂, R₃ and R₄are the same or different and each is C₁ -C₄ alkylene; and Z and Z' areselected independently from H, OH, nitrile ester, halogen and amide. 11.The solvent based thermosetting composition of claim 10, wherein atleast one of Z and Z' bears an hydroxyl group.
 12. The solvent basedthermosetting composition of claim 1, wherein said primary hydroxyfunctional acid is selected from the group consisting ofdimethylolpropionic acid, bis(hydroxy ethyl)propionic acid, bis(hydroxypropyl)propionic acid, and a compatible mixture of any of them.
 13. Thesolvent based thermosetting composition of claim 1, wherein said acidcomponent further comprises fatty acid, said hydroxy functional acid andsaid fatty acid being in molar ratio of from 1:0 to about 1:1,respectively.
 14. The solvent based thermosetting composition of claim13, wherein said fatty acid is selected from the group consisting ofSoya fatty acid, butyric, lauric, palmitic and stearic fatty acid and acompatible mixture of any of them.
 15. A solvent based, thermosettingcomposition in accordance with claim 1, wherein said crosslinking agentconsists essentially of blocked polyisocyanate.
 16. A solvent based,thermosetting composition in accordance with claim 15, wherein saidblocked polyisocyanate is selected from blocked aliphatic, aromatic,cycloalkylene, aliphatic aromatic and nuclear substituted aromaticpolyisocyanates.
 17. A solvent based, thermosetting composition inaccordance with claim 1, wherein said blocked polyisocyanatecrosslinking agent comprises blocked polymethylene polyphenol isocyanatewhich prior to blocking has the formula: ##STR5## wherein x equals 1 to3.
 18. A solvent based, thermosetting composition in accordance withclaim 1, wherein blocked polyisocyanate crosslinking agent is employedwhich comprises the reaction product of an active hydrogen-bearingblocking agent with polyisocyanate comprising isocyanurate ring-bearingpolyisocyanate prepared by cyclotrimerization of diisocyanate.
 19. Asolvent based, thermosetting composition in accordance with claim 18,wherein said blocked polyisocyanate crosslinking agent consistsessentially of blocked trifunctional isocyanurate represented by theformula: ##STR6## wherein each L is selected independently from thegroup consisting of aliphatic, cycloaliphatic and aromatic divalentradicals and B is the residue of said active hydrogen bearing blockingagent.
 20. A solvent based, thermosetting composition in accordance withclaim 1, wherein said polyisocyanate employed in the preparation of saidblocked polyisocyanate crosslinking agent comprises an isocyanateterminated prepolymer prepared by reacting polyol with an excess ofpolyisocyanate.
 21. A solvent based, thermosetting composition inaccordance with claim 1, wherein said crosslinking agent consists ofblocked polyisocyanate prepared by(A) reacting (i) organic diisocyanaterepresented by the formula

    OCN--L'--NCO

wherein L' is selected from the group consisting of aliphatic,cycloaliphatic and aromatic radicals and combinations thereof andwherein one of the isocyanate groups thereof is substantially morereactive than the other, and (ii) sufficient active hydrogen bearingblocking agent to react with substantially all of said more reactiveisocyanate groups; and (B) reacting the reaction product of (A) withsufficient polyol to react with the remaining isocyanate groups.
 22. Asolvent based, thermosetting composition in accordance with claim 21,wherein said polyol is selected from oligoester diols and triols which(i) have a number average molecular weight (Mn) between about 150 andabout 3,000 and (ii) are the product of esterification reaction betweencarboxylic acid reactant and epoxide reactant, said esterificationreaction product being selected from the group consisting of theesterification reaction product of:(a) polycarboxylic acid andmonoepoxide; (b) polyepoxide and monocarboxylic acid containing noethylenical unsaturation and bearing no hydroxy functionality; (c)hydroxy functional carboxylic acid and monoepoxide; (d) monocarboxylicacid and hydroxy functional monoepoxide; and (e) mixtures of (a)-(d).23. The solvent based, thermosetting composition of claim 1, whereinsaid crosslinking agent consists of hexa(methoxymethyl)melamine.
 24. Anorganic solvent based, thermosetting composition comprising:(A)crosslinkable hydroxy functional epoxy ester resin having a numberaverage molecular weight (Mn) between about 1,000 and about 5,000, saidresin comprising the reaction product of diepoxide reactant selectedfrom the group consisting of bisphenol-A epichlorohydrin epoxy resin,hydantoin epoxy resin, cyclic and acyclic aliphatic diepoxide and acompatible mixture of any of them, with dicarboxylic acid reactantselected from the group consisting of substantially saturated, acyclicaliphatic dimer acids of 4-42 carbons and a compatible mixture of any ofthem and primary hydroxy functional organic acid selected from the groupconsisting of dimethylolpropionic acid, bis(hydroxy ethyl)propionicacid, bis(hydroxy propyl)propionic acid and a compatible mixture of anyof them; and (B) blocked polyisocyanate crosslinking agent comprising atleast two isocyanate groups which have been blocked by reaction with anactive hydrogen bearing blocking agent, said blocked polyisocyanatebeing selected from blocked aliphatic, aromatic, cycloalkylene,aliphatic aromatic, and nuclear substituted aromatic polyisocyanates andbeing included in said composition in an amount such that uponde-blocking of the blocked isocyanate groups thereof at the curetemperature of the composition, said crosslinking agent will providebetween about 0.5 and about 1.6 reactive isocyanate groups per reactivehydroxy group of said epoxy ester resin.